1. Field of the Invention
This invention relates generally to a chilled water system, and, more particularly, to a method and apparatus for extracting make-up water from a main air compressor.
2. Description of the Related Art
The technology explosion in the manufacturing industry has resulted in many new and innovative manufacturing processes. Today's manufacturing processes, particularly industrial-type manufacturing processes, call for a large number of important steps. These process steps include transporting material, such as water and gas, about various locations of the manufacturing arena.
Many industrial applications call for the use of a chilled water system for cooling various liquids and gases used in industry applications. Many times, water systems are designed such that the flow of water may be controlled to cool the water and/or air that is exposed to the flow of the water. Many plants use cooled water and/or cooled air for various industrial applications. Often, water towers and cooling towers are employed to create a flow of water to implement chilled water systems. These flows of chilled water require considerable energy and produce excess water and/or gas, e.g., water in a gaseous state. Many industrial applications today do not utilize all of the available byproducts available from traditional chilled water systems.
In general, state of the art chilled water systems in air separation plants call for circulating a stream of cooling water through a nitrogen chill tower and/or a refrigeration unit to chill the water (e.g., chill water down to about 50-55° F.). This chilled water is then used to cool the air (typically after the aftercooler) prior to entering molecular sieve beds. The chilled water may come in direct contact with the air through a direct contact aftercooler or simply cool the air through a standard shell and tube exchanger. Once the chilled water has cooled the air, it is returned back to a self-contained water tower.
When water is circulated over a nitrogen chill tower, some of the water is evaporated. Owing to the nature of the evaporative process, the evaporating water leaves behind any dissolved solids contained therein. Thus, the dissolved solid content of the remaining liquid has a greater concentration of dissolved solid content. Some chilled water systems use cooling water as a source of make-up water. However, the problem with this approach lies in the fact that the dissolved solid content in this water is generally near a tolerable level. Using the cooling water as the make-up source coupled with the additional evaporation/concentrating effect in the chilled water loop can result in high saturation of the dissolved solids and precipitation. This could result in the formation of scales in various components of the chilled water system. The scaling, which results from saturation of the dissolved solids, may accumulate on the interior of various vessels of the chilled water system. This accumulation may result in packing of the scales, which may cause an increase in the pressure differential across the vessel. The increased pressure differential in various vessels of the water system may result in inefficiencies in heat transfer. Excessive accumulation of scale in the various components of a chilled water system generally requires replacement of the packing material.
A number of approaches to prevent or reduce accumulation of scaling may be implemented. However, each of these potential solutions promotes other problems in the efficient operation of the system. Excessive blow-down processes may be performed to reduce the amount of contaminants in water, concentration of scaling in the chilled water system. However, this practice requires additional cooling water to be sent to the chilled water system to compensate for the excessive blow-down. Often, this excessive blow-down results in the cooling tower operating with less than desirable concentration levels of dissolved solids. This approach may also result in an increase in water and chemical consumption for the cooling tower system, thereby reducing the operating efficiency of the chilled water system.
Acid feed implementations may be performed to counteract and increase alkalinity (pH) in the chilled water system, thereby reducing the potential for scaling formation. However, this approach presents problems, such as safety concerns and environmental issues. In addition, some dissolved solids, such as silica, may still precipitate even at the lower operating pH.
Another attempt to reduce scaling problems involves using the same make-up water source for the chilled water loop that is used to supply the cooling tower. However, this approach also presents problems. Due to contaminants in the make-up water, implementing a complete chemical feed system for pH control (acid) and inhibitor(s) may be necessary. This approach results in having to manage two cooling water systems that will require the same chemical treatment schemes. This may result in increased chemical costs and other equipment costs to perform the chemical treatment processes. Additionally, detrimental safety and environmental issues may exist in employing the current chemical systems used to reduce scaling and other problems in the current chilled water systems.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.